Help with ADA Flanger Rev 03—have a short somewhere

[eurekaiv]

So I've finished up the ADA flanger and I've got a short somewhere on the board it seems.  I can't get any proper voltage readings anywhere due to this.  I've triple and quadruple checked all my offboard wiring and everything comes up golden and at this point I've wired up enough boxes that I'm pretty confident I did things correctly there.  I've also gone back over my board and made sure every cap is oriented properly and every part is in the right place and other then finding two resistors swapped (who's values you very close anyway)  and fixing those, the board is loaded up perfectly. There is no power protection diode in this circuit to look to either and I've checked all my on board diodes and they seem ok...  one 914 is passing 5.15v where most are up around 5.7 however—not sure if this is a problem or not.  None of them checked out open with my meter.  The battery, nor any of the ICs are getting hot but R62 is.  I've pulled one R62 that looked pretty smoked but even after I pulled it, it measured right at the 47Ω it's supposed to.  None of the other resistors from V+ seem to be getting toasty.  Anyone have any suggestions for things to look for?

[oldschoolanalog]

Check to see if C26 is shorted (bad cap).
When you say "the battery" what exactly do you mean? This circuit was really meant to be powered by an 18VDC power supply.
Keep us posted...
Dave

[eurekaiv]

Oh, well, I've got two 9Vs wired up to 18V but it's spitting out a solid 19v from two fresh batteries. Would that be too much and burn something out?  C26 is fine.

[oldschoolanalog]

2 fresh 9V batteries @ 19V should be OK  for testing purposes. They will get eaten up rather quickly though (I discovered this the first time I fired up my Moose rev 1 ). The 7815 reg can handle 35 VDC input, so your supply V shouldn't be a problem. I know this is a PITA, but posting some voltages will be necessary for any serious troubleshooting. Lots of folks have completed this build successfully so I'm sure you'll get plenty of help.
Hang in there.
Dave

[eurekaiv]

Oh, I'd be more then happy to post voltages but since my supply is trickling down to ground somewhere I can't even get an accurate voltage reading to use that as a troubleshooting measure.  If I could I probably would have already had this figured out.    I did check all my V+ voltages on the board prior to installing my ICs and everything looked kosher at that point.  Is it possible I had a bad IC from the get go?  I'm pretty well versed in troubleshooting circuits but I've never had an IC fail and I'm not sure how to go about testing other then make sure no pins are open to ground... other then the ones that should be of course.

[slacker]

What I would do is remove all the ICs, that's assuming you've socketed them, and then try and measure the voltage on all the pins of the 7815 and at pin 14 of of IC2. You should have something like this
7815 pin1 18volts
7815 pin2 0volts
7815 pin3 15volts

IC2 pin14 7.5volts

If any of those voltages are off then you must have a short or an incorrect or faulty component value somewhere.
If those voltages look Ok try putting IC3 back in and measure them again. The fact that R62 was getting hot possibly means IC3 is faulty or there a problem somewhere round IC3. Do the same thing with the rest of the ICs, that way if one of them is faulty you'll find out which one.

Hope that helps.

[eurekaiv]

With all ICs removed V+ is spot on and not dropping.  Vb on the other hand is 20millivolts and that's what I'm getting at IC2 pin 14 and all other Vb locations.

[slacker]

Sorry I'm an idiot, with IC2 removed you won't get 7.5 volts on pin14. You should get about 7.5 volts where the 2 68k resistors meet, which I think is pin12 of  IC2. If you then install IC2 you should get 7.5volts at all the vb points.

[StephenGiles]

What I suggest you do having first established the vb voltage, is insert the ICs in the audio and trace for a good audio signal at each IC before the BBD. If there is no output at any IC, then thoroughly check for solder bridges, incorrect components etc. If all is OK, insert a signal after the BBD and do the same again. If that is all OK, check the LFO is working and manual CV area, right up to where it hits the 4047. I have to go to a meeting now, but do you get my drift? Check each section of the circuit separately.

[eurekaiv]

Yeah, I defenitely catch your drift.    I think I'm going to take a few days away from this one and get some other stuff done as I've been looking at it a bit too much...  I should have been able to find that voltage divider and figure out the Vb thing myself.